[llvm] [LV] Add initial legality checks for early exit loops with side effects (PR #145663)

[Florian Hahn via llvm-commits]

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@@ -1813,6 +1840,99 @@ bool LoopVectorizationLegality::isVectorizableEarlyExitLoop() {
                        "backedge taken count: "
                     << *SymbolicMaxBTC << '\n');
   UncountableExitingBB = SingleUncountableExitingBlock;
+  UncountableExitWithSideEffects = HasSideEffects;
+  return true;
+}
+
+bool LoopVectorizationLegality::canUncountableExitConditionLoadBeMoved(
+    BasicBlock *ExitingBlock) {
+  // Try to find a load in the critical path for the uncountable exit condition.
+  // This is currently matching about the simplest form we can, expecting
+  // only one in-loop load, the result of which is directly compared against
+  // a loop-invariant value.
+  // FIXME: We're insisting on a single use for now, because otherwise we will
+  // need to make PHI nodes for other users. That can be done once the initial
+  // transform code lands.
+  auto *Br = cast<BranchInst>(ExitingBlock->getTerminator());
+
+  using namespace llvm::PatternMatch;
+  Instruction *L = nullptr;
+  Value *Ptr = nullptr;
+  Value *R = nullptr;
+  if (!match(Br->getCondition(),
+             m_OneUse(m_ICmp(m_OneUse(m_Instruction(L, m_Load(m_Value(Ptr)))),
+                             m_Value(R))))) {
+    reportVectorizationFailure(
+        "Early exit loop with store but no supported condition load",
+        "NoConditionLoadForEarlyExitLoop", ORE, TheLoop);
+    return false;
+  }
+
+  // FIXME: Don't rely on operand ordering for the comparison.
+  if (!TheLoop->isLoopInvariant(R)) {
+    reportVectorizationFailure(
+        "Early exit loop with store but no supported condition load",
+        "NoConditionLoadForEarlyExitLoop", ORE, TheLoop);
+    return false;
+  }
+
+  // Make sure that the load address is not loop invariant; we want an
+  // address calculation that we can rotate to the next vector iteration.
+  const SCEV *PtrScev = PSE.getSE()->getSCEV(Ptr);
+  if (!isa<SCEVAddRecExpr>(PtrScev)) {
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fhahn wrote:

(same when other comments have been addressed, there appear to be  no email notifications when reacting with emojis, so there won't be any notifications when the comments have been addressed and it is ready for another look)

https://github.com/llvm/llvm-project/pull/145663